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Auto merge of #97480 - conradludgate:faster-format-literals, r=joshtriplett

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improve format impl for literals

The basic idea of this change can be seen here https://godbolt.org/z/MT37cWoe1.

Updates the format impl to have a fast path for string literals and the default path for regular format args.

This change will allow `format!("string literal")` to be used interchangably with `"string literal".to_owned()`.

This would be relevant in the case of `f!"string literal"` being legal (https://github.com/rust-lang/rfcs/pull/3267) in which case it would be the easiest way to create owned strings from literals, while also being just as efficient as any other impl
This commit is contained in:
bors 2022-05-30 17:39:58 +00:00
commit 4a8d2e3856
1 changed files with 9 additions and 4 deletions
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13
library/alloc/src/fmt.rs
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@ -604,9 +604,14 @@
#[cfg(not(no_global_oom_handling))]
#[must_use]
#[stable(feature = "rust1", since = "1.0.0")]
#[inline]
pub fn format(args: Arguments<'_>) -> string::String {
let capacity = args.estimated_capacity();
let mut output = string::String::with_capacity(capacity);
output.write_fmt(args).expect("a formatting trait implementation returned an error");
output
fn format_inner(args: Arguments<'_>) -> string::String {
let capacity = args.estimated_capacity();
let mut output = string::String::with_capacity(capacity);
output.write_fmt(args).expect("a formatting trait implementation returned an error");
output
}
args.as_str().map_or_else(|| format_inner(args), crate::borrow::ToOwned::to_owned)
}